1. Field of the Invention
The present invention relates to a method and apparatus for preparing a femur to receive a prosthetic femoral component. More particularly, the present invention relates to a method and apparatus for preparing a femur to receive a modular prosthetic femoral component having a discrete proximal body and a discrete distal stem.
2. Description of the Related Art
Orthopaedic implants utilized to replace all, or a portion of, a patient""s joint (e.g., the hip) are commonly utilized to restore the use of, or increase the use of a joint which has deteriorated due to, e.g., aging, illness, or injury. In the case of hip replacement, femoral components are utilized to replace a portion of the patient""s femur including, e.g., the femoral head and neck. Prior to implantation of the femoral component, the patient""s femur must be prepared to receive same.
Preparation of the femur entails excising a portion of the femur generally consisting of the femoral head and femoral neck (if this portion of the femur is intact). After removal of this portion of the femur, an elongate channel (i.e., femoral canal) of sufficient diameter to receive the prosthetic femoral component is formed in the femur. Typically, the elongate channel is formed utilizing a reamer to progressively bore through the femur until the desired depth is achieved. Some surgical techniques utilize a rasp either in addition to, or in lieu of reaming to prepare the femoral canal to receive the prosthetic femoral component. Many prosthetic femoral components are formed as an integral component having a femoral stem component sized whereby formation of the entire depth of the femoral canal with a single instrument, e.g., reamer, is appropriate.
In addition to the one-piece femoral components described above, modular femoral components utilizing a discrete proximal body together with a discrete distal stem have been developed. Such modular femoral components provide great flexibility to surgeons performing a total, or partial hip arthroplasty. Relatively few modular components may be utilized to form a relatively large number of versatile use femoral components. Furthermore, the modularity of these components allows for substantially infinite version adjustment when positioning the proximal body on an implanted distal stem. Modular femoral components are typically designed to achieve sufficient distal stem fixation in the femur (i.e., fixation of the distal stem to the femur) so that fixation of the proximal body is unnecessary. This is particularly advantageous in situations in which the femur has undergone extensive bone loss and therefore fixation of the proximal body is not possible.
Utilization of a modular femoral component requires that the proximal portion of the femoral canal be of larger diameter than the distal portion of the femoral canal. The distal portion of the femoral canal is generally sized so that the distal stem of the modular femoral component can be interference fit therein, while the proximal portion of the femoral canal is made large enough so that it will not interfere with the passage of the distal stem therethrough. Furthermore, many modular femoral components utilize a proximal body having a stem portion of greater diameter than the distal stem component. With this in mind, the proximal portion of the femoral canal must be of greater diameter to accommodate the proximal body. Additionally, it is desirable to size the proximal femoral canal to accommodate rotation of the proximal body about the distal stem (prior to affixation of the proximal body to the distal stem) so that version adjustment can be effected.
When utilizing modular prosthetic femoral components, imprecision in canal sizing can take the form of either over sizing, or under sizing. In cases of over sizing, portions of the femoral canal into which the distal stem will be seated will be oversized and, therefore, will not function to provide an interference fit with the distal stem. Since modular femoral components rely upon fixation of the distal stem, such over sizing is undesirable. Additionally, over sizing results in unnecessary bone removal. Under sizing is problematic because it will cause the distal stem to get hung up in the femoral canal prior to achieving the desired depth, which will make seating of the distal femoral component more difficult.
What is needed in the art is a method and apparatus for preparing a femur to receive a modular prosthetic femoral component which allows for precision in proximal and distal sizing.
The present invention provides an improved method and apparatus for preparing a femur to receive a modular prosthetic femoral component. A distal reamer is utilized to prepare the distal femoral canal and thereafter remains in the femoral canal during proximal sizing. The proximal canal sizing or forming tool, e.g. a reamer or rasp, is cannulated and is sized to fit about the shank of the distal reamer. Proximal sizing is effected with the distal reamer in place in the femur and a mechanical stop is utilized to control proximal sizing depth. The mechanical stop eliminates proximal over and under sizing. Preferably, the proximal sizing tool is a reamer.
The invention, in one form thereof, comprises an apparatus for preparing a femur to receive a modular prosthetic femoral implant. The apparatus of this form of the current invention includes a distal reamer having a distal reaming head and a shank as well as a cannulated reamer or rasp sized to fit about the shank of the distal reamer. A mechanical stop limits the travel of the cannulated reamer when the cannulated reamer is placed about the shank of the distal reamer.
The invention, in another form thereof, comprises, in combination, a modular prosthetic femoral implant set for replacing a portion of a femur and an apparatus for preparing the femur to receive a modular prosthetic femoral implant formed from the implant set. A distal femoral stem is seated in a femoral canal prepared by a pair of reamers. A distal reamer reams the femoral canal to receive the distal femoral stem and includes a distal reaming head and a shank. A cannulated reamer is sized to fit about the shank of the distal reamer and includes a proximal reaming head sized to ream a proximal portion of the femoral canal, whereby the distal femoral stem will pass through the proximal portion of the femoral canal without interference. A mechanical stop limits the travel of the cannulated reamer when the cannulated reamer is placed about the shank of the distal reamer. The mechanical stop prevents the cannulated reamer from reaming into an area of the femoral canal into which the distal femoral stem will be seated.
The invention, in yet another form thereof, comprises a method of preparing a femur to receive a modular prosthetic implant. The method of this form of the current invention includes the steps of: providing a distal reamer having a distal reaming head and a shank, the distal reamer having a mechanical stop associated therewith; reaming the femur with the distal reamer; providing a cannulated proximal sizing tool sized to fit about the shank of the distal reamer; with the distal reamer left in the femur, placing the cannulated sizing tool about the shank of the distal reamer; and advancing the sizing tool into the femur to form the proximal femoral canal to receive the proximal body component, whereby the mechanical stop limits the travel of the cannulated sizing tool.
The present invention advantageously eliminates the possibility of proximally over sizing or under sizing the femoral canal.